This application claims benefit of Japanese Application No. 2000-135028 filed in Japan on May 8, 2000, the contents of which are incorporated by these references.
1. Field of the Invention
The present invention relates to a camera distance measuring device, and particularly to a camera distance measuring device which illuminates a photographic object if required and measures the distance thereto.
2. Related Art Statement
Conventionally, various camera distance measuring devices have been proposed, and known as such distance measuring methods are the trigonometrical survey method and the spectrum time detection method. Among these methods, the trigonometrical survey method is generally employed with cameras, and this trigonometrical survey method can be classified broadly into a passive method and an active method.
A typical distance measuring device employing the aforementioned passive method is structured, for example, of a pair of line sensors which separates light from the photographic object into a pair of light images, and receives and converts such light into electrical signals, respectively. Moreover, when the luminance or contrast of the photographic object is low, the distance measuring device may also comprise an auxiliary light source such as a strobe light for irradiating illumination light toward the photographic object. In this passive method, it is possible to precisely measure the distance even if the photographic object is distant, and it is further possible to measure the distance extensively within the photography range when the photographic object is bright and the contrast of the photographic object is sufficient. In contrast, when the luminance or contrast of the photographic object is low, it becomes difficult to accurately measure the distance when the illumination by the aforementioned auxiliary light source is insufficient.
Moreover, a typical distance measuring device employing the aforementioned active method comprises, for example, an IRED for projecting an infrared light beam toward a photographic object and a PSD for receiving the reflected light from the photographic object to which the aforementioned infrared beam was irradiated. As this active method is basically for projecting infrared light in a beams shape, it is possible to accurately measure the distance to the photographic object even if the object itself has little contrast. In contrast, it is difficult to accurately measure the distance when the photographic object is so distant that the infrared light is not reached, and, in addition, it is only possible to measure the distance to the photographic object positioned near the center of the photography range.
It could be said that the passive method and active method are in a supplemental relationship where the demerit of one method is supplemented by the merit of the other. Thus, in recent years, a high-performance hybrid measuring device has come into practical application by fusing the passive method and active method and supplementing the demerit of one method with the merit of the other.
This hybrid distance measuring device comprises, for example, a pair of line sensors and a projection means, and its basic structure is nearly the same as a basic structure of the passive distance measuring device. Moreover, the hybrid distance measuring device also employs the same phase difference calculating (correlative calculation) as a distance measuring device of the aforementioned passive method upon finding the distance to the photographic object.
The difference between the hybrid method and passive method is that a fixed light elimination circuit is added for each pixel constituting the line sensor. In other words, this hybrid distance measuring device will function as a passive distance measuring device by turning the aforementioned fixed light elimination circuit off, and function as an active distance measuring device by turning the fixed light elimination circuit on.
When turning the fixed light elimination circuit on and making it function as an active distance measuring device, the line sensor receives the light emitted from a projection means such as an infrared LED and reflected from the photographic object. Then, by eliminating the fixed light component with the aforementioned fixed light elimination circuit from the output from the respective pixels of the line sensor, it is possible to abstract the component illuminated by the infrared LED. And, by performing phase difference calculating (correlative calculation) thereto, it is possible to find the distance to the photographic object.
The most important factor which determines the performance of the aforementioned hybrid distance measuring device is, of course, the sensor, but secondly important is the projection means. An ideal projection means comprises a projection element with a large light volume and capable of illuminating light in a wide range.
Nevertheless, the aforementioned ideal projection means, in other words, a projection means with a large light volume and capable of illuminating light in a wide range as well as being miniature so as to be capable of being mounted on a camera, unfortunately, does not exist at present. Therefore, it is necessary to either provide with a projection means separately or to reduce the light volume and mount it on the camera, and it was not possible to maintain the compactness and measure distances with high precision under a broad range of situations.
Accordingly, an object of the present invention is to provide a miniature camera distance measuring device capable of measuring distances with high precision under various circumstances.
Simply, the present invention is a camera distance measuring device, which comprises: brightness determination means for determining the brightness of a photographic object; first illumination means for illuminating a range containing at least a photography range of the camera; second illumination means for illuminating a part of the range contained within the photography range of the camera; at least a pair of integral light receiving means having a plurality of pixels and fixed light elimination means corresponding to the respective pixels; integration mode switching means for switching the integration mode of the integral light receiving means by controlling the operative state of the first illumination means, second illumination means and fixed light elimination means; calculating means for finding the distance to the photographic object based on object image signals obtained by the integral light receiving means; and distance measuring inability judgment means for determining whether it is possible to measure the distance by judging the reliability of the output of the calculating means; wherein, when the brightness determination means determines that the photographic object is bright, distance is measured in the first distance measuring mode by the integration mode switching means making the first illumination means, second illumination means and fixed light elimination means inoperative, the integral light receiving means integrating in the second integration mode, and the calculating means finding the distance to the photographic object based on the obtained object image signals; wherein, when the brightness determination means determines that the photographic object is dark, distance is measured in the second distance measuring mode by the integration mode switching means making the second illumination means inoperative and making the first illumination means and fixed light elimination means operative, the integral light receiving means integrating in the second integration mode, and the calculating means finding the distance to the photographic object based on the obtained object image signals; and wherein, when the distance measuring inability judgment means judges the reliability of the distance to the photographic object sought with the calculating means and the result thereof is that distance measuring is impossible, distance is measured in the third distance measuring mode by the integration mode switching means making the first illumination means inoperative and making the second illumination means and fixed light elimination means operative, the integral light receiving means newly integrating in the second integration mode, and the calculating means finding the distance to the photographic object based on the obtained object image signals.
The present invention is also a camera distance measuring device having fixed light elimination means and which functions as an active distance measuring device by making the fixed light elimination means operative and which functions as a passive distance measuring device by making the fixed light elimination means inoperative, comprising: first illumination means for illuminating a range containing at least a photography range when functioning as an active distance measuring device; and second illumination means for illuminating a part of the range contained within the photography range and which becomes operative alternatively with the first illumination means when functioning as an active distance measuring device.
The object(s) and advantages of the present invention will become further apparent from the following detailed explanation.